While recharging of primary batteries is frequently discouraged by battery manufacturers, as discussed in detail in each of Applicant's copending applications listed above, which are incorporated by reference in their entireties herein, under certain conditions, primary batteries can be recharged.
As disclosed in the listed Applicant's copending applications, novel battery chargers have been developed by applicant which are capable of recharging primary zinc-manganese dioxide alkaline cells, rechargeable alkaline manganese (R.A.M.) cells, nickel cadmium cells, and to the extent that they are rechargeable, conventional standard and heavy duty "dry cells". The critical parameters relating to the charging of each type of cell or battery are charging current, cut-off voltage, temperature coefficient of cut-off voltage, and short and long reverse pulse patterns, i.e., their duration, repetition rate and current.
While the battery chargers described in Applicant's copending applications have enabled successful recharging of primary zinc-manganese dioxide alkaline batteries, rechargeable alkaline manganese cells, nickel cadmium cells, and conventional standard and heavy duty "dry cells", there has been a problem caused by the rising internal impedance of certain primary alkaline cells as a function of increasing state-of-charge. While there are many possible theories to explain this effect, and its variability from cell to cell, and from charge cycle to charge cycle, the fact is that on the average, the internal impedance does rise as the state of charge rises above from about a third of available capacity. It has also been observed that fixed voltage float and/or alternating current (A.C.) components including those from an A.C. charge current component or from charge/discharge activity, do tend to progressively raise internal impedance, even when the cell is near available capacity and no significant net charging is occurring.
The problem of rising internal impedance as a function of increasing state-of-charge is particularly acute when recharging primary ZnMnO.sub.2 alkaline batteries which are constructed of essentially non-recombinant cells. Therefore, if charge storage efficiency (the fraction of the charging current which is stored and available for discharge) declines with rising state of charge (as it does for all cells), then a rising fraction of the incoming current produces non-equilibrium reactions which are not indefinitely sustainable and which lead to cell evolution, generally in an undesirable direction.